The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An all wheel drive method of a vehicle driving both front and rear vehicle shafts may be generally divided into two types: a switched all wheel drive type and a continuous all wheel drive type.
The switched all wheel drive continuously drives only one vehicle shaft and transfers drive force to the residual vehicle shafts only if required, and the continuous all wheel drive continuously drives all wheels by the drive force of an engine.
Meanwhile, in an on-demand type all wheel drive system, durability of a clutch is generally designed to coincide with durability of a power transmissions system, but a damage degree of the clutch varies depending on a used load in an actual use area, and as a result, the durability of the clutch may be shorter than durability as designed.
In particular, when a slip amount and transfer torque of the clutch exceed a durability design criterion, the durability of the clutch is shorter than the designed durability by 10 to 15% so that unexpected situations which may occur while a vehicle is actually driven cannot be properly prepared. Under the situations, we have discovered that it is difficult to accurately measure actual durability of the clutch and in particular, when the vehicle is continuously driven as being deviated from a durability limit of the clutch, a damage risk of the clutch degrades power transmission performance in the all wheel drive system, of course.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.